This invention relates to an esophageal probe and more particularly to a probe for transesophageal monitoring of cardiac activity and transesophageal stimulation of the heart, such as cardiac pacing or electroversion (cardioversion or defibrillation).
Transesophageal probes have been adapted for producing echo-cardiograms, measuring transesophageal ECG's, for use as transesophageal stethoscopes, and to achieve transesophageal cardiac monitoring, pacing and cardiac electroversion. It has been determined that transesophageal probe monitoring, pacing and electroversion can provide an attractive alternative to existing invasive (transvenous or epicardial) and non-invasive (transcutaneous) methods of cardiac stimulation.
It has been widely demonstrated that transesophageal atrial pacing (TAP) can be successfully performed in a substantial majority of anesthetized patients. However, TAP is not possible nor helpful in patients experiencing atrial fibrillation or complete A-V heart block. In these cases, temporary ventricular pacing is required to alleviate bradycardia occurring in combination with rhythm disturbances. For this reason, it would be desirable to perform indirect transesophageal ventricular pacing (TVP) as an alternative to the existing invasive (transvenous or epicardial) or non-invasive (transcutaneous) methods for cardiac stimulation. Unfortunately, the success rate of TVP capture using conventional and known transesophageal probes is much lower than the incidence of capture with TAP.
One attempt to solve the problem of TVP capture employs an esophageal probe having a stimulating electrode mounted on an inflatable balloon. When the electrode is deemed to be appropriately positioned in the esophagus and adjacent the posterior wall of the left ventricle, the balloon is inflated by means of an air supply conduit extending through the esophageal probe. Inflation of the balloon lodges the electrode in place in the esophagus. While this technique provides an increased incidence of TVP capture by reducing the esophageal-posterior left ventricular distance and providing adequate electrode contact, it has not been wholly satisfactory. If the balloon is over-inflated, or left in place for an extended period of time, the concentrated circumferential force of the balloon overpressure on the esophageal mucosa can cause damage to the tissue. In the alternative, if the balloon is not sufficiently inflated and the esophageal-posterior left ventricular distance is not adequately reduced, a higher energy stimulating pulse is necessary to achieve TVP capture. Under these circumstances, extended use of TVP with a pulse energy which is higher than ideal might also cause damage to the esophageal tissue. Each of these effects are undesirable, particularly in patients suffering from circulatory shock consequent to severe bradycardia.
An alternative to the balloon mounted electrode is to use a conventional esophageal stethoscope having surface mounted electrodes. However, because of the reduced contact between the electrode and the esophageal mucosa, and the increase in the distance between the esophagus and the posterior wall of the left ventricle, stimuli having higher current and longer pulse durations must be supplied to the electrode. Once again, this poses the risk of damage to the esophageal tissue.
Thus, it is desirable to provide an esophageal probe that can provide reliable TVP capture while reducing the risk of damaging the esophagus.